The present invention is directed in general to amplified speakers, of the type in which an amplifier is directly mounted on or within the enclosure of an electroacoustic speaker.
Amplified speakers are used mainly in applications where a local amplifier is limited in output power. Examples are the amplified speaker V-1020 C and other models marketed by Valcom of Roanoke, Va. The amplified speaker increases the capabilities of the local amplifier by providing remote amplification of signals at the speaker using AC power available at that location and on-board amplifiers that require very little of the power of the local amplifier.
Amplified speakers also find use in applications not requiring a local amplifier or where a local amplifier is not available, such as in various telephone applications. For example, many PABXs have what are called 600 Ohm ports which act as extensions where it is possible to connect the input of an amplified speaker via a twisted pair to call u the extension and initiate a page message. In such a case, a local amplifier is not required, since the amplified speaker may be hooked up directly to the 600 Ohm port.
The amplified speakers which are currently available commercially, while providing satisfactory operation in general, have certain drawbacks and operational limitations which render them less than desirable for all applications. In particular, presently available amplified speakers are expensive, are characterized by inefficient power transfer which limits the number of speakers capable of being powered from one power source and are typically capable of accommodating only a standard 30 mVrms to 1 Vrms (600 Ohms) audio source. These disadvantages result from the fact that currently available amplified speakers operate from an expensive 24 volts DC regulated power supply and that the input audio signal matching is limited to the standard 600 Ohm telephone signal levels only. In addition to being expensive, the regulated power supply also has an inherent inefficient power transfer characteristic, thereby limiting the number of speakers capable of being powered from the power source.